The present invention falls within the field of aeronautical equipment. It concerns more specifically deicing devices. In this case, it relates in particular to the problem of deicing propeller blades.
During the various phases of flight, particularly on the ground, at take-off, climbing or landing, aircraft are regularly subjected to icing atmospheric conditions (cold surface+ambient humidity), which cause ice deposits to be created on various parts of the fuselage. These ice deposits modify the aircraft's aerodynamic performance, increase its mass and reduce its maneuverability.
Various anti-icing devices (that prevent ice forming on a surface of the aircraft) and deicing devices (that detach pieces of ice once they have formed) have been developed over decades and are already known to experts. For example, for the leading edges of wings, they use heating resistors that cause the ice to melt and to break into pieces removed by the airflow. In the same way, inflatable membranes are used intermittently to break ice while it is forming.
It is obvious that similar problems of fighting icing by anti-icing or deicing occur for the propeller blades in the case of propeller-driven airplanes. In this case, heating resistors are generally used, with an electrical generator installed in the propeller shaft and a transfer of current towards cables passing through this shaft towards the various blades (see patent document WO 97/24261, for example).
The amount of power required to ensure permanent deicing of the blades then leads to the preferred choice of heating the blades one after the other, in cyclical fashion. This mode of deicing at regular intervals reduces the electrical power needed and the size of the generator.
In contrast, in the case of propulsion units known under the generic name “propfan”, comprising two counter-rotating propellers with an open rotor (not faired) driven by a differential gearbox which is itself driven by a turbomachine, the propellers are arranged in annular fashion around the core of this turbomachine and this arrangement prevents the use of the devices mentioned previously.
Rotating contact devices are known in addition that ensure the transmission of electrical power between a fixed shaft and a moving annular part by using electro-conductive brushes fixed on the shaft that slide on an annular track of the rotating part.
In this case, the power to be transferred to device the blades of a propfan is close to some twenty kilowatts, which implies devices of significant size. One of the main drawbacks of these rotating contact systems is linked to the speed of the brushes in relation to the moving track, this speed being in general close to one hundred meters per second and depending naturally on the diameter of the annular track and on the speed of rotation of this part.
The consequence of this for all these rotating contact systems is rapid wear of the brushes, leading to reduced performance and a requirement for frequent and costly maintenance. The absence of lubrication for these brushes (for reasons of complexity) also contributes to reducing this lifespan significantly.
In the case of the front propeller of a propfan, the diameter of the turbomachine's core leads to a relative speed of the moving part in relation to the stationary part of the order of four hundred meters per second, which makes systems using brushes and a moving track unusable in practice, as this exceeds the specifications of devices available on the market.
The situation is further exacerbated in the case of propfans by the counter-rotating characteristic of the two propellers.
Lastly, propfans are characterized by the high temperature of the exhaust flow they generate, about 800° C. at the outlet; this gas flow passes between the propulsion unit's shaft and the two propellers and makes it difficult to install materials that may suffer in high-temperature conditions.